Enter the flow or the number of fixtures, the pressure needed at the critical outlet and the heights. The page computes booster head, parallel pumps with standby, motor size, drive savings and tank volume.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Parallel pumps at fixed speed versus the constant pressure held by the drive.
Fixed speed (pumps staged in cascade) and drive holding design pressure.
Take this page’s results to another calculator with the fields already filled in.
The calculation report gathers this page's inputs, results, equations, assumptions and references, with fields for project, engineer and revision. The full report also includes the charts and interpretations, in color. In the print dialog, choose Save as PDF.
A set of pumps that raises water pressure when the city main or tank cannot provide enough pressure at the highest or farthest outlets. In buildings, plants and campuses it replaces or supplements a gravity tank. It usually has two or more pumps in parallel with standby, pressure-switch or VFD control and a small tank.
Measured peak-hour flow is best. In the US, plumbing codes size domestic water by Hunter’s fixture-unit method (IPC/UPC tables); enter that flow directly. The simple simultaneity option here uses K = 1/√(n − 1): 200 fixtures of 3 gpm at about 7% give 42.5 gpm. For plants, add up equipment that runs at the same time.
Add the pressure needed at the critical outlet, the elevation to it and the friction losses, then subtract the pressure already available at the suction. In the example: 25 psig at the outlet, 60 ft of elevation and 15 ft of losses, minus 3 psig of suction, give 126 ft and 57.5 psig at the discharge. Losses can come from the valve and fitting pressure drop calculator.
The most common arrangement is n + 1: duty pumps cover design flow and one stands by, with automatic alternation. Splitting flow between two or three duty pumps improves efficiency at low demand and allows maintenance without cutting water. In the example, 2 + 1 pumps of 21 gpm with 1.5 hp motors.
In most cases, yes: the drive holds constant pressure, avoids overpressure at low demand and cuts starts. In the example, at fixed speed pressure climbs to 71 psig when demand drops, still under the 80 psi IPC limit, and the drive saves 14% of energy, about $145 a year. Savings grow the more time demand stays low.
With on/off control, the tank limits starts per hour: in the example, 64 gal for up to 30 starts per hour with a 15 psi switch band. With a drive, the tank only holds pressure during zero-demand periods and is usually much smaller; follow the package manufacturer. The hydropneumatic tank calculator details that volume.
Overestimating design flow, which leaves big pumps running far from their best point; forgetting maximum pressure at the lowest outlets; and not protecting pumps against dry running. This calculator uses a typical centrifugal pump curve: confirm the selection on the manufacturer’s real curve and check NPSH.
Important notice: Indus Metrics tools produce estimates and pre-sizing results from the data you enter and from published engineering methods. They do not replace design, calculations or reports signed by a licensed professional engineer (PE), nor verification against the applicable codes, standards and regulations, such as OSHA rules and the ASME codes. Material and fuel properties vary: check manufacturer data or your own process analyses before deciding. By using this site you agree to the Terms of Use.
© 2026 Indus Metrics. Found an error? Write to contato@seudominio.com.